When you go into their details, do you have a little red check mark next to the skill you want them to perform the most? Having that selected makes them autonomously perform actions they're good at more often. So if you have masters with the skill they master in selected they SHOULD be doing it on their own.

Now, keep in mind there have been reportings of lazy villagers and stupid ones too! My gang is pretty self sufficient and hard working but I'll catch them standing around, relaxing, dancing and exercising! If they've been working hard I allow them the break

Check your details first - if that isn't it maybe they are just being lazy!